In recent years, a liquid crystal display device has been generally used which is capable of realizing a high image quality thereby performing display using a local dimming technique.
FIG. 10 is a diagram illustrating a function of a local dimming control circuit provided with a liquid crystal display device.
As illustrated in the drawing, full HD image data (image data of a 2K1K size) is input to a local dimming control circuit 50, and backlight luminance data, which is the luminance data of each area in the backlight is calculated in the local dimming control circuit 50, and is output to a backlight driving circuit 51. In addition, in the local dimming control circuit 50, gradation data of each pixel for the full HD (2K1K size) is calculated using the backlight luminance data and the above-described full HD image data, and is output to a liquid crystal driving circuit 52.
In other words, the local dimming control circuit 50 is configured to determine the gradation data of each pixel by adding the backlight luminance data.
There is no particular problem in a case where the image data of the 2K1K size as the image size that may be processed is input to the local dimming control circuit 50 in which the image size that may be processed is fixed to the 2K1K size.
Incidentally, the image data of the 2K1K size is image data of approximately horizontal 2000 pixels×vertical 1000 pixels. Specifically, a representative example is image data of 1920×1080.
However, in a case where, for example, UHD image data (image data of a 4K2K size) as an image size that is not assumed is input to the local dimming control circuit 50 in which the image size that may be processed is fixed to the 2K1K size, there is a need for providing an additional processing circuit (a backlight luminance distribution estimation circuit, a liquid crystal luminance calculation circuit or the like) to the outside in order to perform the process, calculate the gradation data of each pixel for the UHD (4K2K size) and output the gradation data to the liquid crystal driving circuit, which causes complexity in the process and increase in the process time and cost.
Incidentally, the image data of the 4K2K size is image data of approximately horizontal 4000 pixels×vertical 2000 pixels. Specifically, a representative example is image data of 3840×2160 dots, 4096×2160 dots, 4096×1776 dots, 3300×2160 dots and the like.
FIG. 11 is a diagram illustrating a circuit configuration of the related art provided with the local dimming control circuit 50, which may process the UHD image data (the image data of the 4K2K size) as the image size that is not assumed and in which the image size that may be processed is fixed to the 2K1K size.
As described above, the local dimming control circuit 50 is configured to calculate the gradation data of each pixel using the backlight luminance data and the full HD image data. Meanwhile, the backlight luminance data is also required for each pixel unit in terms of granularity, and a memory is required for storing each data, but in general, the image size that may be processed is fixed in the specification so as to reduce the cost.
As illustrated in FIG. 11, in a case where the image data of the 4K2K size is processed using the local dimming control circuit 50 in which the image size that may be processed is fixed to the 2K1K size, first, the image data of the 4K2K size is input to a down-converter 53 and converted to image data of the 2K1K size.
Further, the image data of the 2K1K size converted by the down-converter 53 is input to the local dimming control circuit 50, the luminance data (a control block size of the local dimming) of each area of the backlight and the gradation data (2K1K size) of each pixel are calculated in the local dimming control circuit 50, and the unnecessary gradation data (2K1K size) of each pixel is discarded without being used.
Incidentally, the backlight luminance data is output in the block size of the backlight (for example, in a case where the division number is horizontally 24 divisions and vertically 12 divisions, the data size of 24×12 blocks) and is supplied to the backlight driving circuit 51, and is also supplied to a backlight luminance distribution estimation circuit 54.
In the backlight luminance distribution estimation circuit 54, the backlight luminance data of the block size is converted to the backlight luminance distribution data (4K2K size) by estimation of luminance distribution (superimposing the luminance distribution on the entire block in accordance with the luminance distribution of each block using the input backlight luminance data of the block size and backlight illumination distribution of one block that is measured or estimated in advance), and the backlight luminance distribution data is supplied to a liquid crystal gradation calculation circuit 55.
Then, the liquid crystal gradation calculation circuit 55 calculates the gradation data (4K2K size) of each pixel based on the image data of the 4K2K size input to the down-converter 53 and the backlight luminance distribution data (4K2K size) to be supplied from the backlight luminance distribution estimation circuit 54, and the gradation data is supplied to the liquid crystal driving circuit 56.
FIG. 12 is a diagram specifically illustrating a process performed by the local dimming control circuit 50, the down-converter 53, the backlight luminance distribution estimation circuit 54 and the liquid crystal gradation calculation circuit 55 illustrated in FIG. 11.
Hereinafter, a description will be made regarding a method of the related art in which the liquid crystal gradation data of the 4K2K size is obtained from the input image data of the 4K2K size with reference to FIG. 12.
First, the input image data of the 4K2K size is reduced into reduced image data for local dimming (2K1K size) by the down-converter 53.
Incidentally, a method that is generally known may be employed as a reduction method, and any method of a nearest neighbor method, a linear interpolation method, quadratic interpolation, cubic interpolation, an average pixel method, and the like may be employed. It is possible to obtain a reduced result VI1 by any one of the above-described methods (for example, the linear interpolation method) from 4K2K-size input image data Vi1 to Vi4, and it is possible to obtain a reduced result VI2 from 4K2K-size input image data Vi5 to Vi8 in the same manner.
As described above, it is configured to obtain one reduced image data for the local dimming by reducing pixel data having an aspect ratio of 2×2 of the 4K2K-size input image data.
Then, reduced image data for the local dimming VI1, VI2 and so on are processed by the local dimming control circuit 50, and backlight luminance data VB1, VB2 and so on are output.
Then, 4K2K-size backlight luminance distribution data Vd1, Vd2, . . . , Vd8 and so on are obtained by the backlight luminance distribution estimation circuit 54 from the illumination distribution of one block obtained from the backlight luminance data VB1, VB2 and so on, which are the luminance values of one block of the backlight sought from the pixel group of the input image data of 2×2.
Further, it is configured to calculate the final 4K2K-size liquid crystal gradation data Vo1, Vo2, . . . , Vo8 and so on by the liquid crystal gradation calculation circuit 55 based on the luminance value corresponding to each pixel position of the backlight luminance distribution data Vd1, Vd2, . . . , Vd8 and so on, and the corresponding gradation value of each pixel of the 4K2K-size input image data Vi1 to Vi8 and so on.
Meanwhile, FIG. 13 is a block diagram illustrating a schematic configuration of a liquid crystal display device 100 which performs display by dividing an image disclosed in Patent Literature 1 into four areas of upper left, upper right, lower left and lower right.
As illustrated in FIG. 13, the liquid crystal display device 100 is provided with a control device 101, a liquid crystal display panel 102 and a backlight unit 103.
Further, the control device 101 is provided with a preprocessing circuit 110, dividing circuits 111a and 111b, upscaling circuits 112a to 112d, a down-converter 113, compensating circuits 114a to 114d, a liquid crystal driving circuit 115, a display map generating circuit 116, an LED resolution signal generating circuit 117, an luminance distribution data generating circuit 118, an LED driving circuit 119, and switches SW1 and SW2a to SW2d. 
In such a circuit configuration, in a case where an image having a size larger than the image size that may be processed by the LED resolution signal generating circuit 117 is input, the compensating circuits 114a to 114d which calculate the gradation data to be output to the liquid crystal driving circuit 115 are capable of processing the image size that may be processed by the LED resolution signal generating circuit 117, and are configured to receive the input image divided by the dividing circuit 111a or the input image output from the dividing circuit 111b and processed by the upscaling circuits 112a to 112d, and the backlight luminance distribution data created by the luminance distribution data generating circuit 118.
Further, the backlight luminance distribution input to the compensating circuits 114a to 114d uses data from the common LED resolution signal generating circuit 117, and thus, it is possible to realize a high image quality using continuous emission distribution and the gradation data in accordance with the continuous emission distribution as compared to a simple multi-display.